1. Field of the Invention
The present invention relates to a method for compacting concrete in a mold.
2. Description of the Prior Art
Methods for fabrication of concrete elements by using different types of molds are known in the prior art. The molds are generally fabricated of steel, wood, concrete, or some other stiff plate material. The molds are dimensioned to withstand the casting pressure during concrete pouring and compaction without appreciable deformation. In addition, the molds must be capable of being dismantled after the concrete has set. When the molds are assembled and stiffly supported, the casting proper can be started. The casting is generally carried out by loading concrete into the mold in small quantities by vibrating the mold simultaneously or by using separate vibrators for compaction. Filling the mold is continued by adding concrete in small quantities until the mold is filled up to the rim and the upper surface can be smoothed. Various vibrating methods are applied in prior art casting procedures, according to mold size, shape and concrete mix stiffness.
Common vibrators are of the high-frequency vibrating type, which are stiffly mounted to the mold and integrally transfer the vibration energy to the cast concrete. Especially with molds of light construction, another conventional method is to use a high-frequency vibrator rod which is transported or transferred according to the progress of the casting process to the point where compaction is desired.
Combinations of the aforementioned methods are also used in the prior art. Equally well known is the procedure of applying a method known as shock compaction in horizontally cast elements to compact concrete by sharp blows at a low repetition rate.
However, all the aforementioned methods and equipment suffer from the following drawbacks:
In all vibrating methods, which utilize high-frequency vibration, the process generates high-intensity acoustic noise that is difficult to attenuate or eliminate. Also in the shock method, the noise level is high due to the high impact energy. In addition, the transfer of vibration energy from the vibrators to the concrete mix requires extremely stiff mold constructions to allow the vibration energy to spread sufficiently far into the mix, or when using molds of light construction, several vibrators must be used. All these arrangements result in high vibration forces, heavy mold constructions, and simultaneously a low efficiency of energy utilization in compaction. Furthermore, the high acoustic noise level exceeds generally accepted limit values if no acoustic damping countermeasures are provided, leading to health hazards.